Flash as2 Need help with my function() code please

programming flash
1

Below is my code. All I am trying to do is, when I press the SPACE key, the character doesn’t keep going up. The spacebar is acting like a turbo button. If I press the space bar once, the character jumps, if I hold down the space bar, the character continues to keep going up. How to I make this so when the player presses the space or holds down the space, you will only execute a jump?

class Hero extends MovieClip
{
    var velocity;
    var isJumping;
    var jumpSpeed;
    var startY;
    
    function onLoad()
    {
        velocity = 10;
        isJumping = false;
        jumpSpeed = 0;
        startY = _y;
    }
    
    function onEnterFrame()
    {
        if(Key.isDown(Key.RIGHT))
        {
            this.gotoAndStop(2);
            _x = _x + velocity;            
        }
        else if(Key.isDown(Key.LEFT))
        {
            this.gotoAndStop(3);
            _x = _x -+ velocity;
        }
        else
        {
            this.gotoAndStop(1);
        }
        
        if(isJumping)
        {
            _y += jumpSpeed;
            jumpSpeed += 1;
            if(_y >+ startY)
            {
                _y = startY;
                isJumping = false;
            }
        }
        
        if(Key.isDown(Key.SPACE))
        {
            isJumping = true;
            jumpSpeed = -5;
        }
    }
}